In this work a newly developed surgical procedure in non-human primates will be employed in concert with a novel high sensitivity stable isotope tracer technique to investigate the transport and conversion of alpha- linolenic acid (ALA) and its bioactive 22 carbon product docosahexaenoic acid (DHA) during pregnancy. Evidence is now accumulating to suggest visual response in preterm infants is linked to the dietary supply of DHA early in postnatal life. While adults are capable of converting ALA to DHA, little information on the timing of enzymatic activity required to convert ALA to DHA relative to birth and in particular premature birth is available. Pregnant baboons are chronically catheterized in the maternal and fetal vasculature and maintained for 10 or more days on a tether and swivel. Either mother or fetus receives a dose of 13C-labeled ALA or DHA, retroconversion of DHA, interconversion into non-essential fatty acids, and net placental transport, will be determined at the beginning and at the peak of the brain growth spurt. Net incorporation of ALA, DHA, and their metabolic products into fetal retina and rod outer segments, cerebrum and cerebellum, and the site of most active lipid metabolism, the liver, will be determined. Net bioequivalence of ALA as a DHA precursor will be investigated under dietary conditions where ALA is marginal. Lipid classes in which fetal fatty acids are transported will be identified and determined quantitatively at two critical stages of the brain growth spurt, onset and peak.